The cored sponge model of in vivo leucocyte chemotaxis

A Haptotaxis Assay for Neutrophils using Optical Patterning and a High-content Approach

Neutrophil recruitment guided by chemotactic cues is a central event in host defense against infection and tissue injury. While the mechanisms underlying neutrophil chemotaxis have been extensively studied, these are just recently being addressed by using high-content approaches or surface-bound chemotactic gradients (haptotaxis) in vitro. Here, we report a haptotaxis assay, based on the classic under-agarose assay, which combines an optical patterning technique to generate surface-bound formyl peptide gradients as well as an automated imaging and analysis of a large number of migration trajectories. We show that human neutrophils migrate on covalently-bound formyl-peptide gradients, which influence the speed and frequency of neutrophil penetration under the agarose. Analysis revealed that neutrophils migrating on surface-bound patterns accumulate in the region of the highest peptide concentration, thereby mimicking in vivo events. We propose the use of a chemotactic precision index, gyration tensors and neutrophil penetration rate for characterizing haptotaxis. This high-content assay provides a simple approach that can be applied for studying molecular mechanisms underlying haptotaxis on user-defined gradient shape.

Evaluation of chemokine- and phlogistin-mediated leukocyte chemotaxis using an in vivo sponge model

We have directly compared the in vivo activity of a number of chemokines and phlogistins using a modified murine in vivo sponge model in which gelatin sponges are soaked with chemoattractant and implanted in the peritoneal cavity. Sponges soaked with murine JE/MCP-1 (monocyte chemoattractant protein-1) or zymosan promoted the chemotaxis of specific leukocyte populations in a time-dependent manner, as judged by multiparameter flow cytometry, with granulocytes predominating in zymosan-soaked sponges and granulocytes and macrophages present in JE/MCP-1-soaked sponges. Smaller numbers of B, T and dendritic cells were identified as well. Eotaxin selectively chemoattracted eosinophils in this model, while MIG induced significant T cell migration relative to other chemokines. Cell migration was inhibited by administration of methotrexate, piroxicam or dexamethasone, and JE/MCP-1-mediated trafficking was impaired by treatment with anti-JE antibody or with IL-10, suggesting a role for pro-inflammatory factors in amplifying the JE/MCP-1-induced response. This amplification phase involves the production of the chemokine KC, since anti-KC antibody significantly attenuated JE/MCP-1-induced chemotaxis. These results indicate that intraperitoneally implanted chemoattractant-soaked gelatin sponges are capable of inducing a pronounced inflammatory response characterized by the selective migration of leukocyte populations, and suggest that this model may be useful for delineating the activity of novel inhibitors of leukocyte chemotaxis.

Enzymes degrading bacterial chemotactic F-met peptides in human ileal and colonic mucosa

Bacterial chemotactic F-met peptides have been identified in culture supernatants of intestinal bacteria and in human faecal dialysates. These potent inflammatory agents could play a role in intestinal inflammatory disorders should they cross the epithelial barrier of the gut. We have identified mucosal peptidases which degrade F-met-leu-phe (FMLP) in ileal and colonic mucosal biopsies obtained at colonoscopy. A carboxypeptidase, inhibited by D-L-benzyl succinate (BzS), accounted for more than 60% of total FMLP-ase activity, other uncharacterized peptidases contributing the rest of the activity against the intact peptide. An F-met deformylase, inactive against di- and tri-peptides, cleaves released F-met completing the degradation. Total FMLP-ase, carboxypeptidase and F-met deformylase activities were measured in serial mucosal biopsies from 15 control patients undergoing colonoscopy for occult bleeding with negative findings and from 15 patients with ulcerative colitis (UC) and 10 with Crohn's disease (CD). Highest activities were found in terminal ileum and lowest in the rectum. Total FMLP-ase and carboxypeptidase activities were similar in controls and UC patients but were substantially reduced in CD, especially in the terminal ileum (controls 493 +/- 146 and 116 +/- 73 nmol/100 micrograms protein per h, respectively and CD 231 +/- 96 and 41 +/- 36 nmol/100 micrograms protein per h, respectively (P = 0.0018 and 0.015). F-met deformylase activities were similar in all groups. There was no correlation between enzyme activity and severity of inflammation. FMLP degrading peptidases probably contribute to the mucosal barrier of the gut in regions of high bacterial colonization, limiting intestinal absorption and inflammatory responses to these potent bacterial products in the intestinal lumen.

Partial purification and characterization of a formylmethionine deformylase from rat small intestine

A formylmethionine deformylase from rat small-intestinal mucosa has been isolated, characterized and partially purified. The enzyme catalyses the release of equimolar amounts of formate and the free amino acid. The deformylase was active against formylmethionine (Km 7.1 mM) and formylnorleucine, but showed reduced activity against formyl-leucine. It was inactive against a range of other polar and nonpolar formyl-amino acids and against formyl di- and tri-peptides. The Mr of the native enzyme was between 45,000 and 66,000, as determined by h.p.l.c. gel permeation. Further purification of the enzyme either by h.p.l.c. ion-exchange chromatography and concanavalin A-Sepharose or by isoelectric focusing yielded a preparation with one predominant band of Mr 50,000 on SDS/polyacrylamide-gel electrophoresis. Bacteria in the intestine present the host with substantial amounts of formylmethionine (fMet) from proteinase and carboxypeptidase digestion of bacterial formyl-peptides in the intestinal lumen. fMet (0.01-1.0 mM) inhibited translation of a test RNA from brome mosaic virus in vitro, indicating that it could have adverse effects on cellular metabolism. Gut epithelial fMet deformylase may be required for deformylation of this exogenous (bacterial) and also endogenous (mitochondrial) fMet.

Enterohepatic circulation of bacterial chemotactic peptide in rats with experimental colitis

The association of hepatobiliary disorders with colonic inflammation is well recognized. Although the pathophysiology is obscure, increased permeation of toxic bacterial products across the inflamed gut to the portal circulation might be one mechanism. Potentially toxic metabolites include N-formylated chemotactic peptides that are produced by several species of intestinal bacteria and can be detected in colonic fluid in vivo. To investigate the metabolic fate of one of these low molecular weight proinflammatory peptides, N-formyl L-methionine L-leucine 125I-L-tyrosine was introduced into colon loops of healthy rats (n = 10) and rats with experimental colitis (n = 15) induced by rectal instillation of 15% (vol/vol) acetic acid. Gut, liver, and blood radioactivity were monitored by external gamma-counting and radioactivity in bile was measured by biliary catheter drainage into a well counter. Bile was processed by high-performance liquid chromatography to determine the amount of intact, bioactive peptide excreted over 3 h. After colonic instillation of 1 nmol of peptide, the mean (+/- SEM) biliary excretion of intact peptide was 6.4 +/- 2.0 pmol in normal rats and 49.0 +/- 20 pmol in rats with colitis (p less than 0.01). An enterohepatic circulation of synthetic N-formyl L-methionine L-leucine L-tyrosine has been demonstrated in the rat. Experimental colitis was associated with an eightfold increase in biliary excretion of this proinflammatory bacterial peptide. Proinflammatory bacterial peptides synthesized by colonic bacteria could be important in the pathophysiology of colon inflammation and its frequently associated hepatobiliary complications.